MX2012006085A

MX2012006085A - Preform for producing plastic containers in a two-stage stretch blow-moulding process.

Info

Publication number: MX2012006085A
Application number: MX2012006085A
Authority: MX
Inventors: Robert Siegl
Original assignee: Alpla Werke
Priority date: 2009-12-23
Filing date: 2010-10-02
Publication date: 2012-11-12
Also published as: CH702464A1; ES2461965T3; EP2516121B1; US20120231191A1; BR112012013893A2; WO2011076301A1; BR112012013893B8; RU2012131428A; CN102695591B; US8617676B2; PL2516121T3; BR112012013893B1; PT2516121E; RU2540301C2; CN102695591A; EP2516121A1; CA2784644A1; UA106407C2; HRP20140490T1

Abstract

The invention relates to a preform (1) for producing plastic containers in a two-stage stretch blow-moulding process, wherein the preform has an elongated preform body (2), the one longitudinal end of which is closed by a bottom (3), while the other longitudinal end adjoins a neck section (4) having threaded sections (5) or similar positive protrusions. The preform (1) is produced from a plastic material suited for the stretch blow-moulding process, said material having a refractive index of 1.3 to 1.6 at a temperature of 100Â°C to 120Â°C. The preform bottom (3) is designed such that the outer wall (18) thereof and the inner wall (17) thereof delimit a flat divergent lens. The outer wall (18) and the inner wall (17) of the preform bottom (3) designed as a divergent lens have radii of curvature (c, b) which are greater at least by a factor of 1.4 than the radii of curvature (s, r) of the associated outer wall (8) or inner wall (7) in the region of the preform body.

Description

PREFO JA TO PRODUCE PLASTIC CONTAINERS IN A MOLDING PROCEDURE BY BLOWING AND STRETCHED IN TWO STAGES Description of the invention The invention relates to a preform for producing plastic containers in a blow-molding process and stretching in two stages according to the preamble of claim 1.

A large number of plastic containers that are used today - in particular, for example, plastic flasks and the like - are produced in a blow-molding and drawing process. In this method, what is termed a preform - which in most cases has a shape similar to elongated tube and has a base at one of its longitudinal ends and a neck region with shaped or similar threaded sections in the another longitudinal end - is inserted into a mold cavity of a blow mold and is blown through a medium that is injected with overpressure. In this case, the preform is further extended in the axial direction with an elongated mandrel that is inserted through the neck opening. After the elongation / blow molding process, the finished plastic container is demolded from the blow mold.

The single or multiple layer preform usually Ref. : 230741 is produced in a separate injection molding process before the blow-molding and drawing process. It has also already been proposed to produce preforms in a plastic extrusion pressing method. As a raw material for the production of plastic containers in the process of blow and stretch molding, polypropylene or PET (polyethylene terephthalate) is mainly used. Polypropylene and PET have been tested multiple times and their properties are well known. In the so-called single-stage stretch blow molding process, the preform is inflated and elongated directly after its production to form a plastic container. However, in many cases the plastic containers are produced in a two-stage method at a different time and place in the blow-molding process and are intermittently stored for later use. In the last stretch blow molding process, the preforms are heated again, introduced into a blow mold, stretched with an elongated mandrel in the longitudinal direction and inflated according to the mold cavity by overpressure to form a plastic container. In this way, both methods - injection molding and die-casting and stretching - can be operated separately and optimally.

The preforms that are used in the blow-and-stretch molding method usually have an elongated shape and have a convex base that curves outwardly. The neck region of the preform has already been completely shaped and is provided with threaded sections or similar positive projections which make it possible to join a closure or cover, which is equipped with correspondingly designed locking elements. In the two-stage process, the preforms need to be heated again to the deformation temperature range before blow-molding and stretching. To this end, the preforms are sealed with their neck regions within finger-like fastening devices and transported through a heating station. In many cases, the heating of the preforms is carried out via infrared radiation or near infrared radiation, which is generated by radiators of quartz tubes. For a better use of the energy emitted by the quartz tube radiators, one or more mirrors reflecting the electromagnetic radiation are provided. In the heating station, the preforms are transported between the quartz tube radiators and the mirrors facing them. Through the pump base of the preform, the irradiated infrared radiation moves by dispersion or directly uniformly towards the gripping devices similar to fingers of the preforms, which in this way are heated. To thereby avoid deformations of the neck region of the preform that is shaped with high precision, the finger-like fastening devices must be cooled. Since the radiated energy absorbed frequently can not be removed by draining to a sufficient degree even by the cooling devices of the fastener, the neck of the preform must often be designed with a wall thickness greater than that required for the container of plastic that must be manufactured from the preform. During blow-molding and stretching, the preform is stretched longitudinally using an elongated mandrel. In the region of the support surface of the base of the preform with the elongated mandrel, the base is cooled relatively quickly and an undesirable buildup of amorphous material may occur in the base region of the plastic container that is produced in the process of blow-molding and stretching.

The object of this invention is therefore to correct these drawbacks of the preforms of the state of the art. A preform will be provided which makes it possible to design the neck region also with reduced wall thickness. In the further processing of the preform to form a plastic container in the two-stage blow-molding process, undesirable accumulations of amorphous material in the base region of the container should be avoided.

These additional objects are obtained according to the invention by a preform with the features that are eliminated in claim 1. Further developments as well as advantageous embodiments and preferred variants of the invention are the subject of the dependent claims.

A preform for producing plastic containers in a two stage blow molding and stretching process is proposed by the invention, and the preform has an elongated preform body whose longitudinal end is sealed with a base and the other longitudinal end of which is a neck section with threaded sections or similar positive projections are connected. The preform is made of a plastic that is suitable for the blow and stretch molding process which has a refractive index of 1.3 to 1.6 at a temperature of 10 ° C to 120 ° C. The base of the preform is desi in such a way that its outer wall and its inner wall delimit a flat divergent lens. The outer wall and the inner wall of the base of the preform that is desi as a diverging lens in this case have radii of curvature that are larger by at least a factor of 1.4 compared to the radii of curvature of the outer wall or the related inner wall in the region of the preform body.

In combination with the refractive index of the material of the preform, the configuration of the preform base as a flat diverging lens causes the irradiated electromaic heat radiation to be deflected away from the finger-like holding device. By configuring the preform body according to the invention, the absorption of a greater proportion of the electromaic heat radiation introduced into the base of the preform and the wall of the preform is carried out. As a result, less radiation energy arrives at the finger-like clamping device of the preform during its transport through the heating station and the clamping device heats up less considerably. The neck portion of the preform, which is in direct contact with the finger-like clamping device in this manner, is also heated less. As a result, the risk of a deformation of the neck portion is considerably reduced and there is the possibility of designing the neck portion with a smaller wall thickness. The decrease in wall thickness of the preform in the neck portion leads to a reduction in the costly raw material. Specifically, in mass-produced articles such as plastic containers, a reduction of material has economic or also ecological advantages.

In general, the design according to the invention results in a flattening of the base of the preform. As a result, during the stretching process, there is first only a small region to form a contact between the elongated mandrel, whose front end has a small radius of curvature, and the base of the preform with a comparatively large radius of curvature . Only at very high elongation speeds and pressures and toward the end of the mechanical elongation process is this contact region increased. As a result, the local cooling of the preform base is limited to a very small region and undesirable accumulations of amorphous material can be avoided in the base region of the plastic container that is produced. Instead of this, the plastic material not yet cooled in the base of the preform is available for the remainder of the blow molding process. This also makes possible a reduction of material in the base of the preform.

In a variant embodiment of the invention, the base of the preform that is designed as a planar diverging lens in the region of the axis of the preform or in the center of the diverging lens has a wall thickness that is at least 0.2 mm less than the wall thickness of the base of the preform in the transition in the body of the preform.

The base of the preform is configured in particular so that an electromagnetic heat radiation of a wavelength of 0.5 μ ?? at 2 μt ?, which is introduced into the region of the base essentially perpendicular to the axis of the preform is absorbed to a significant degree by the total reflection within the base and / or body of the preform. In this way it is ensured that very little electromagnetic radiation reaches the finger-like clamping device and the neck portion which is in contact with the clamping device is heated in a smaller amount. By a larger proportion of the heat radiation introduced which is absorbed at the base of the preform and / or in the body of the preform, the heating efficiency of the preform is also increased.

The base of the preform can be designed in a flat-concave or convex-concave manner. In this case, the terms "plane" or "convex" are related to the first surface on which the electromagnetic radiation is carried out, that is, to the outer wall of the base of the preform. The term "concave" is related to the opposite inner wall of the base of the preform. The outer wall of the base of the preform will have a greater radius of curvature than the inner wall of the preform in the region of its base. In the case of a flat design of the outer wall, the radius of curvature is infinitely large.

The preforms which are designed in accordance with the invention and are provided for further processing in a two-stage stretch blow-molding process advantageously consist of plastics or plastics mixtures of the group consisting of polyester, PET (acronym in English for polyethylene terephthalate), polyolefins, polystyrenes and PLA (acronyms in English for polylactic acids).

The preform according to the invention can be constituted of one or more layers depending on the application provided. It may also comprise barrier additives, in particular oxygen traps, nanoclays or UV blockers. In another variant embodiment of the invention, the preform that is made up of multiple layers can also have an oxygen barrier layer and / or UV radiation and / or a sliding coating and / or residual waste coating.

The preform according to the invention is produced, for example, in a plastic injection method. Plastic injection methods or injection molding methods have been sufficiently tested and result in preforms with the desired precision. In this case, the feeding point of the preform is suitably located in the region of the base. In the plastic container that is produced from the preform, in this way it is generally not visible in the deployed position.

The plastic extrusion press method represents an alternative production method for the preform, which also leads to high quality results and is very suitable for mass production.

The preform that is designed according to the invention can also be produced in a blow molding and extrusion method. This production method has already been used recently to an increasing degree and is distinguished by its high yield and low production costs and is also suitable in particular for preforms that are made up of multiple layers. Multilayer preforms can also be produced in the so-called "overmoulding" method.

The preform that is designed according to the invention can be provided at least in places with a color that deviates from the usual preform body or can have at least one color layer in a variant multilayer embodiment. The variable coloration or the color layer can also be used, for example, to absorb - even better and specifically in the preform material - the radiation energy that is introduced when the preform is heated.

In another variant embodiment of the preform, it can also be provided that the latter has an outer wall in its base region that has a greater roughness than the outer wall of the body of the preform. The increased roughness can also be used for better absorption of the radiation energy introduced into the preform material.

A variant embodiment of the preform that is useful in relation to the reduced use of material has a neck portion which has - in the region of the threaded sections or in similar positive projections - a minimum wall thickness that is smaller in size. less 20% than the average wall thickness in the preform body region.

In another variant embodiment of the invention, the neck portion in the region of threaded sections or similar positive projections, in particular on the threaded base, has a minimum wall thickness that is less than 1.34 mm.

The plastic containers, which are manufactured in a two-stage stretch blow-molding process, constitute a preform that is designed according to the invention, in many cases it has a better and more homogeneous material distribution compared to the containers of conventional plastic of the state of the art and therefore has more uniform properties of resistance in relation to mechanical and thermal stresses, for example, in applications in which the content is supplied hot.

The additional advantages and the variant modalities of the invention follow from the description below of a modality with reference to the grammatical figures. Here, the figures are not to scale: Figure 1 shows a preform according to the invention in an axial section on the half of one side in the heating station; Y Figure 2 shows a preform according to the invention in an axial section on the half of one side.

Figure 1 shows diagrammatically a preform with the half of an axially cut side, which is generally provided with the reference number 1 during its transport through a heating station 30. The preform 1 has an elongated preform body 2 whose longitudinal end is sealed with the preform base 3. A neck portion 4 on which the outer threaded section 5 or the like is made is connected to the opposite end section of the preform body 2. The threaded sections 5 or the like allow the screwing of a closure or cover which is equipped with corresponding locking elements. The preform 1 is produced, for example, in a plastic injection method or in an extrusion press method. It can also be produced in a blow molding and extrusion method. The preform 1 is an intermediate product of a two-stage stretch blow-molding process in which first the preform 1 is produced and, at a different time and place, the preform is reformed by axial stretching and radial inflation to form a plastic container. The method of blow molding and stretching in two stages has the advantage that the production of preform and production of the plastic container can be carried out independently of each other, in each case, with an optimum clock speed.

So that the preform 1 can be stretched in the blow and stretch molding device and can be inflated by overpressure, it must first be heated again to a temperature that is necessary for the blow-molding and stretching process. For this purpose, it is transported through one or more heating stations 30. The heating station 30 comprises several heat lamps, usually quartz tube radiators 31, which emit electromagnetic radiation R in the near infrared and infrared ranges. The wavelength of the emitted radiation is in the range of 0.5 μp? at 2 μp ?. Usually several radiators 31 of quartz tube are distributed one over the other. A reflector 32 distribution, for example metal reflectors are provided oriented towards the quartz tube radiators 31 which reflect the electromagnetic radiation R that is emitted by the quartz tube radiators. The preform 1 is transported through a channel between the quartz tube radiators 31 and the reflector distribution 32. For this purpose, the first head with a neck portion 4 on the finger-like holding device 35 is plugged, which are continuously transported or synchronized through the heating station 30. Usually, in this case, the finger-like clamping device 35 also rotates about its axis so that the preform 1 is heated on all sides. The finger-like holding device 35 moves under a stationary or movable dilution 33 which is provided with a slit-like opening 34 for the preform 1. The division 33 is to prevent the heating of electromagnetic radiation R of the radiators 31 of quartz tubes or from the mirror array 32 preventing it from moving to the finger-like clamping device 35 and the neck portion 4 of the preform 1. In most cases, the clamping device 35 similar to fingers is further provided with a coolant, for example, water coolant to prevent it from overheating. Due to this heating, the neck portion 4 of the preform 1 which is manufactured with high precision and which is in indirect contact with the finger-like fastening device 35 can otherwise be softened and deformed.

Due to the division 33, relatively little electromagnetic radiation reaches the finger-like clamping device 35. The preform base highly in the form of a pump represents a problem, however, in the preforms of the state of the art. This leads to the fact that the electromagnetic heat radiation that is introduced into the base region is moved by diffraction and multiple reflections to the finger-like holding device 35 and warms the latter. To correct this problem, the preform 1 according to the invention is made of a plastic which is suitable for the blow-molding and stretch process and which has a refractive index of 1.3 to 1.6 at a temperature of 10 ° C to 120 ° C. The preform base 3 has an inner wall 17 and an outer wall 18 defining a flat diverging lens. For this purpose, the radii of curvature r, s of the inner wall 17 or the outer wall 18 of the preform base (3) have radii of curvature b, c which are larger by at least a factor of 1.4 compared to the radii of curvature related r, s of the inner wall 7 and the outer wall 8 of the preform body 2. In the region of the axis A of the preform 1, which at the same time forms the center of the diverging lenses, the preform base 3 has a wall thickness that is at least 0.2 mm smaller than in the region of the transfer of the preform 1. body 2 of preform. In particular, the preform base 3 is designed so that the electromagnetic radiation, which is introduced essentially perpendicular to the axis A of the preform, of a wavelength of 0.5 μ? at 2 μp? it is absorbed to a significant degree by a total reflection within the preform base 3 and / or the body 2 of the preform 1.

Figure 2 shows the preform according to the invention which again is referred to in general with the reference number 1 in a presentation that is cut axially in the lateral half. The elongated cylindrical preform body generally has the reference number 2, and the base of the preform has the reference number 3. The neck portion that is adjacent to the preform body 2 has the reference number 4 and the threaded sections are indicated with the number 5. The axis of the preform is provided with the reference letter A. A transfer ring 6 separates the neck portion 4 from the preform body 2. The transfer ring 6 is used to transport and support the preform and the plastic container produced therefrom in certain sections of the blow-molding and stretch-molding device unit. In the region of the preform body 2, the preform 1 has an inner wall 7 as well as an outer wall 8. The inner wall 7 in the region of the preform body 2 has a radius of curvature r. The outer wall 8 of the preform body 2 has a radius of curvature which is provided with the reference numbers s. In the region of the preform base 3, the inner wall is provided with the reference number 17 and the outer wall is provided with the reference number 18. The inner wall 17 in the region of the preform base 3 has a radius of curvature which is indicated as b and the outer wall 18 in the region of the base 3 of the preform has a radius of curvature which is indicated as c.

The preform base 3 is designed according to the type of divergent flat-concave or convex-concave lenses. The terms "plane" or "convex" in this case refer to the first surface on which the radiated electromagnetic radiation strikes, that is, on the outer wall 18 of the preform base 3. The term "concave" is related to the opposite inner wall 17 of the preform base 3. The outer wall 18 of the preform base 3 has a greater radius of curvature c than the inner wall 17 of the preform body. In the case of a flat design of the outer wall 18 of the preform base 3, the radius of curvature c is infinitely large.

Due to the design of the preform base 3 according to the invention, the volume of electromagnetic radiation irradiated in the preform base 3 region of the wavelength of 0.5 μp? at 2 μp? it is absorbed by total reflection into the preform base 3 and / or the body 2 of the preform 1 or is reflected outwards again from the inner wall of the preform 1. The total reflection is carried out with the transition from the medium optically more dense to the optically thinner medium. An electromagnetic radiation that is transmitted from an optically denser medium (a medium with a higher refractive index or) to an optically thinner medium (a medium with a lower refractive index n2) is decomposed according to the refractive law of Snellius on the contact surface of the axis of incidence. The angle of reflection is greater than the angle of incidence of electromagnetic radiation (for example, infrared radiation). If the angle of incidence is increased, the refracted beam, starting at a certain angle, runs parallel to the contact surface. This critical angle is also a total reflection angle. The total reflection angle is obtained as arcsine (n2 / nl). Due to the design of the preform base 3 according to the invention, the volume of the electromagnetic radiation that is radiated flat in the base region is absorbed.

The flat design of the preform base 3 also has advantages over the interaction of the preform base 3 with the elongated mandrel. During blow-molding and stretching, the preform 1 is lengthened using an elongated mandrel in the longitudinal direction. The elongated mandrel has a relatively small radius of curvature at its free front end while the radius of curvature b of the inner wall 17 of the preform base 3 is relatively large. Thus, during the stretching process, it results only in a very small contact area between the preform base 3 and the elongated mandrel. As a result, the preform base 3 is cooled to a lesser degree and the plastic material found therein is additionally available for the blown and stretch molding process.

The preform 1 which is designed in accordance with the invention for further processing in a two-stage stretch blow-molding process consists of plastics which are suitable for the blow-molding and stretch-molding process, which, at a temperature of 10 ° C. ° C at 120 ° C has a refractive index of 1.3 to 1.6, for example, polyester, PET (polyethylene terephthalate), polyolefins, polystyrenes and PLA (acronyms in English for polylactic acids) or mixtures thereof . The preform can be made up of single or multiple layers. It can be provided with additives that are used as barriers against oxygen, water vapor or carbon dioxide and / or fillers.

The preform 1 may have one or more color layers and / or barrier coatings and / or slide coatings and / or residual waste coatings.

Due to the low heating of the finger-like clamping device during transport through the heating station, the neck portion 4 of the preform 1 is also heated to a lesser degree. As a result, it can be designed in the neck portion with a smaller wall thickness than conventional preforms with heavy bases in pump form. In this way, the preforms can be used whose neck portions in the region of the threaded sections or similar positive projections have a minimum wall thickness w that is less by at least 20% compared to the average wall thickness of the preform body region.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A preform for producing plastic containers in a two-stage blow-molding process with an elongated preform body, the longitudinal end of which is sealed with a preform base and the other longitudinal end of which is connected to a neck portion with sections threaded of similar positive projections, characterized in that the preform is made of a plastic that is suitable for a blow-molding and stretching process, which has a refractive index of 1.3 to 1.6 at a temperature of 10 ° C to 120 ° C and wherein the outer wall and an inner wall of the preform base delimit a flat diverging lens and in each case have a radius of curvature that is larger by at least a factor of 1.4 than a related radius of curvature of a wall outside of a radius of curvature of an inner wall of the preform in the region of the preform body.

2. The preform according to claim 1, characterized in that the preform base which is designed as a flat diverging lens has a wall thickness, in the region of the preform axis which is smaller by at least 0.2 mm compared to its thickness of wall in the region of its transition in the body of preform.

3. The preform according to any of the preceding claims, characterized in that its preform base is designed as a plane divergent lens in such a way that the electromagnetic radiation of a wavelength of 0.5 μp? at 2 μ a, which is introduced essentially perpendicular to the preform axis is absorbed to a significant degree by total reflection within the preform base and / or within the preform body.

4. The preform according to any of the preceding claims, characterized in that it is made of a plastic or a plastic mixture of the group consisting of polyester, PET, polyolefins, polystyrenes and PLA.

5. The preform according to any of the preceding claims, characterized in that it comprises one or more multiple layers.

6. The preform according to any of the preceding claims, characterized in that it is produced in a plastic injection method and the injection point is located in the region of the base of the preform.

7. The preform according to any of claims 1 to 5, characterized in that it is produced in a plastic extrusion press method.

8. The preform according to any of claims 1 to 5, characterized in that it is produced in a method of blow molding and extrusion.

9. The preform according to any of the preceding claims, characterized in that it is made up of multiple layers and has at least one color layer.

10. The preform according to any of the preceding claims, characterized in that in its base region, has an outer wall that has a greater roughness than an outer wall of the body of the preform.

11. The preform according to any of the preceding claims, characterized in that the region of the threaded sections or similar positive projections, the neck portion has a minimum wall thickness that is at least 20% lower than the average wall thickness in the region of the preform body.

12. The preform according to any of the preceding claims, characterized in that the neck portion in the region of the threaded section or similar positive projections, in particular in the threaded base, has a minimum wall thickness that is less than 1.34 mm.

13. A plastic container characterized in that it is manufactured in a process of blow molding and stretching in two stages from a preform, according to any of claims 1 to 12.